At medical sites such as surgical operations, medical diagnosis, etc., a fluorescence image is generated in addition to a normal visible light image by administering fluorescent material such as indocyanine green (ICG) or the like into an affected (diseased) part of a body and imaging the affected part, and both the normal visible light image and the fluorescence image are displayed while superimposing these images to observe the affected part. Here, increase of the light amount of the visible light image causes halation whereas increase of the light amount of the fluorescence image degrades visibility. Therefore, it is necessary to adjust the balance in light amount between the visible light image and the fluorescence image.
Under such circumferences, an imaging system having an optical filter for transmitting visible light and fluorescence therethrough with a desired light-amount balance between the visible light and the fluorescence, and an imaging system having an aperture diaphragm for attenuating(adjusting)visible light are known as an imaging system for generating a visible light image and a fluorescence image (see Japanese Patent No. 4,971,816 and International Publication No. WO2011/007461, for example).
However, the above construction has a problem that the optical system is complicated and the efficiency for light utilization is low because the visible light is attenuated.